1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission.
2. Description of the Related Art
As a typical prior-art control system for automatic vehicle transmissions, Japanese Laid-Open Patent Application No. Hei 10 (1998)-184887 teaches supplying oil (ATF) at maximum hydraulic pressure (in full-duty) to a frictional engaging element such as a hydraulic clutch during shift to remove the clutch-stroke play, thereby decreasing the shift shock experienced by the vehicle occupant.
Thus, in the prior art, since the oil at the line pressure is immediately supplied to the clutch, this can advantageously shorten a time to complete removal of the clutch-stroke play. On the other hand, however, when the oil flow rate fluctuates due to the fluctuation of the engine speed or oil pump speed, the time to complete removal of the clutch-stroke play may disadvantageously varied. As a result, the technique may sometimes increase the shift shock until the learning control correction has become effective.
An object of this invention is therefore to overcome the aforesaid problem and to provide a control system for automatic vehicle transmission, which determines the time to complete removal of the clutch-stroke play of a frictional engaging element such as a hydraulic clutch based on at least the input shaft rotational speed such that the clutch-stroke play removal is effected within a less variant period of time and with a good response, thereby decreasing the shift shock effectively so as to improve the feeling of the vehicle occupant.
Another object of this invention is to overcome the aforesaid problem and to provide a control system for automatic vehicle transmission, which determines a preparatory pressure to complete removal of the clutch-stroke play of a frictional engaging element such as a hydraulic clutch based on at lest the input shaft rotational speed such that the clutch-stroke play removal is effected within a lesser variant period of time and with a better response, thereby decreasing the shift shock effectively so as to improve the feeling of the vehicle occupant.
In order to achieve the objects, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting input torque, through any of frictional engaging elements, generated by the engine and inputted by the input shaft to the driven wheels by the output shaft, in accordance with predetermined shift scheduling defining a target gear based on detected operating conditions of the vehicle and the engine, comprising; input shaft rotational speed detecting means for detecting an input shaft rotational speed inputted to the transmission; supply time determining means for determining a supply time to supply a preparatory pressure to one of the frictional engaging elements of the target gear to be shifted to, based on at least the detected input shaft rotational speed; oil amount estimating means for estimating an oil amount in the one of the frictional engaging elements; supply time correcting means for correcting the supply time based on the estimated oil amount; preparatory pressure calculating means for calculating the preparatory pressure to be supplied to the one of the frictional engaging elements within the determined supply time; and hydraulic pressure control circuit for supplying the preparatory pressure to the one of the frictional engaging elements based on the calculated preparatory pressure.